1. Field of the Invention
The present invention relates to a method for etching a lower electrode of a high dielectric film and, more particularly, to a method for etching platinum in which used are an etch gas and a mask having a good etch ratio with platinum when a lower electrode is made of platinum.
2. Discussion of the Related Art
A background method for etching platinum will be described with reference to the accompanying drawings.
Referring to FIG. 1A, a 100 Angstrom thick titanium (Ti) layer and a 100 Angstrom thick titanium nitride (TiN) layer are successively deposited on a silicon insulating film 1 to form a glue layer 2. A 1000.about.1500 Angstrom thick platinum (Pt) layer 3 used as a lower electrode in a capacitor is deposited on the titanium nitride layer.
Referring to FIG. 1B, a 4000.about.5000 Angstrom thick silicon oxide film 4 is formed on the Pt layer 3, used as a hard mask. A photoresist film 5 is coated on the silicon oxide film 4 and patterned with an exposure and development process.
Referring to FIG. 1C, the silicon oxide film 4 is anisotropically etched with the patterned photoresist film 5 serving as a mask.
Referring to FIG. 1D, the Pt layer 3 and the glue layer 2 are etched with the patterned silicon oxide film 4 serving as a mask by appropriately mixing Cl.sub.2 /Ar/O.sub.2 under a low pressure in an MERIE (magnetron enhanced reactive ion etcher) type equipment.
At this time, the maximum etch ratio of the platinum layer 3 and the silicon oxide film 4 is 1.2:1.
The silicon oxide film 4 used as a hard mask is wet-etched by being dipped into HF liquid solution. After etching the silicon oxide film 4, reaction product 6 generated remains on the side of the platinum layer 3 and the glue layer 2. Platinum is 70% of this reaction product 6, and the rest 30% is H, C, and O. This reaction product 6 having a form of a rabbit ear is removed with HCl solution.
However, the background method for etching platinum has the following problems. Since the maximum etch ration of a platinum layer and a silicon oxide film is 1.2:1, the more highly integrated the device is, the thicker the silicon oxide film is. Because there is a limit in increasing the thickness of a photoresist film, patterns of a silicon oxide film may become poor. Due to poor patterns used as hard masks, etch reliability of platinum becomes inferior. Further, since adhesion of a platinum layer and a silicon oxide film used as a hard mask is poor, peeling is generated in patterning a photoresist film and it is thus hard to form a stable platinum layer. Furthermore, since a reaction product formed by reaction of the platinum and the silicon oxide film is of the form of a rabbit ear, it is hard stably to proceed following process steps. This reaction product having the form of a rabbit ear may cause leakage current in capacitors.